Time delay apparatus



Aug. 24, 1943. HOPPER 2,327,791

TIME DELAY APPARATUS Filed Aug. 19, 1941 I /2 L [8% L lo P /3 /6 /7//VVEN7OP A L HOPPER ATTORNEY set of constants and Patented Aug. 24,1943 mun DELAY APPARATUS Andrew L. Hopper, River Edge, N. J.,

Bell Telephone Laboratories,

New York,

N. Y., a corporation of New asslgnor to Incorporated,

York

Application Alll'llst 19,1941, Serial No. 407,410 6Claims. (01.250-27)This invention relates to an improved timing device for securing greateraccuracy, 8. longer interval of time from-a timing circuit havinga givenpotentials applied thereto, or for securing the same interval of timewith a smaller timing condenser and/or charging resistance.

As set forth in United States patent to Lea 1,552,321, granted September1, 1925, a time delay may be secured by the time of discharging andcharging the condenser connected to the control elements of an electrondischarge device. The charge of the condenser is changed through a highresistance. The value of this resistance and the condenser determine thetime required for the potential across the condenser and thus thepotential of the control element of the electron dis charge device toreach the value required to initiate a discharge through it and operatea relay or other device as desired. The arrangement shown in this Leapatent, however, requires the use of two batteries, one for initiallycharging the condenser and the other for discharging the condenser andoperating the electron discharge device.

In accordance with the present invention the charging and dischargingcircuits of the condenser are rearranged so that the condensers arefirst charged in the opposite direction and dis charged and againcharged to the value required to initiate a discharge through theelectron discharging device from a single battery or source ofpotential. Thus, in accordance with this invention substantially all ofthe advantages of the timing arrangement shown in the patent to Lea isobtained with a single battery.

In accordance with another usual arrangement the condenser is normallydischarged. Then when it is desired to initiate the operation of thetiming circuit a potential is applied to the condenser through a highresistance.

In accordance withthe present invention by charging the condenser in thereverse direction then discharging it and charging it in the directionrequired to initiate a discharge through the electron discharge devicethrough a high resistance a considerably greater time delay is securedwith the same size condenser charging resistance and charging battery orpotential.

A further feature of this invention relates to arranging the circuit sothat the filament or heater circuit of the electron discharge device issupplied from the same source of potential and its circuit completed bythe same contacts as initiate the operation of the timing circuit, thatis, in-

itiate first the discharge and then the charge of the condenser.

A further feature of this invention relates to a slight modiflcation ofthe circuit in which no current is taken from the battery or othersource of potential during the idle or normal condition of the circuit.

The foregoing objects and features of this invention, the novel featuresof which are speciflcally pointed out in the claims appended thereto,may be more readily and fully understood by reference to the attacheddrawings in which:

Fig. 1 illustrates a typical embodiment of this invention;

Fig. 2 is a modification of Fig. 1 in which no current is taken from thesourc of potential during the normal or idle condition of the circuit.

Referring now to Fig. 1, it represents an electron discharge device ofany suitabl'e'type. Device [6 has been shown as a three-element device.It is to be understood, however, it may include more elements ifdesired. Device I 6 may be either a high vacuum tube discharge device inwhich the grid or control element maintains control of the discharge oranode current at all times or it may be a so-called gas discharge devicein which the control element will prevent a discharge from occurring butloses control when the discharge has been initiated through the device.The essential requirement of the device it is that in the potential of acontrol element having a very high input impedance should continuouslyor at least initially control the discharge or anode current of thedevice. Th output relay I1 is connected in the anode circuit of tube I 6so that it will be operated when suflicient anode current flows throughdevice It, i. e., when a discharge is initiated through the tube. Relayl! is shown provided with a single set of transfer contacts. These areshown merely for purposes oi. illustration and as is well understood bythose skilled in the art, other contacts may be added to relay l1. Also,various stepping and switching devices may be operated by magnet ll asis well understood.

Condenser I2 is connected in series with resistances l3, l4 and I8between the control element and cathode of tube I6. The purpose of thesevarious resistances will be explained hereinafter. Normally, ground isconnected to the upper terminal of condenser l2 through the upper breakcontacts of relay l0. As shown in Fig. 1, this ground short circuits thehigh resistance H and causes a small current to how through thisresistance at all times. However, the potential of the upper terminalpotential I2 as well as the upper terminal of resistance II will bemaintained in ground potential at this time. The lower terminal ofcondenser I2 is charged to positive battery potential from batterythrough resistance I5, filament or heater of tube I6, resistances I4 andI3 to the lower terminal of condenser IZ. The values of resistances I3,I4 and I5 are such that it requires only a very short time for condenserI2 to be charged to the potential of battery l9. 7

When it is desired to initiate the operation of the timing circuit shownin Fig. 1 relay ID will be Operated in any suitable manner in anysuitable circuit. Relay I0 is provided with a single transfer codecombination, 1. e., a single pole double throw switch. As will bereadily understood by persons skilled in the art relay Ill may beprovided with other contacts for other purposes. However, so far asinitiating the operation of the timing circuit is concerned onlya singletransfer combination is required, that is, a switch member which has twopositions and makes contact with another member in one position and witha third member in the other position.

The operation of relay It] removes ground from the upper terminal ofresistance II and condenser I2. The operation of relay I0 also connectsground to the common terminal of resistances I3 and I4. By connectingground to resistance l4 the filament circuit of tube I6 is completed. Byconnecting ground to the lower terminal of resistance I3 ground is alsoconnected to the lower terminal of condenser I2. Now the lower terminalof condenser I2 had previously been charged to the potential of batteryI9 above ground. In other words, the upper terminal of condenser I2 wascharged to a potential lower than the lower I terminal condenser I2 bythe amount of potential source I9. Thus, when the lower terminal ofcondenser I2 is connected to ground the upper terminal of condenser I2will assume a potential substantially equal to the potential of sourceI9 but in the reverse direction that is below ground potential.

Thereafter condenser l2 will start to discharge through high resistanceII to battery l9.

After condenser I2 has become fully discharged, that is, its upperterminal reaches ground potential, the upper terminal will start tocharge to a positive potential through high resistance I I. After aninterval of time the upper terminal of condenser I2 will reach thepotential required to initiate the discharge through tube I6. 7

The potential required to initiate a discharge through tube l6 will bedetermined by the constants of tube I6 and in addition the value of thesource of potential I9 and also the relative magnitude of resistances I4and I5. Resistance I4 is provided to apply negative bias to tube I6. Theleft-hand terminal of resistance I4 is at ground potential while theright terminal of resistance I4 is at a positive potential whichpotential is dependent upon the voltage drop across resistance I4. Sincethe right-hand terminal of resistance I4 is connected to the cathode oftube IS the cathode will be at a positive potential aboveground. Henceso long as the control element or grid of tube I6 is connected to groundit will be negative with respect to the cathode and thus a negative biaswill be applied to the tube.

When the discharge is initiated through the tube I6 relay I! will beoperated at the desired time delay interval after the operation of relayWhen relay I0 is released it will remove ground from the common junctionof resistances l3 and Hi and interrupt the filament circuit of tube I6.It will also connect ground to the upper terminal of condenser I2. Whenground is connected to the upper terminal I2 the charge on condenser I2will be reversedthrough resistances I3, I4, I5 and the filament of tubeI6. Resistance I3 is included in this path so that the dis chargecurrent of condenser l2 will not be suflicient to injure the heater orfilament of tube IS.

The modification shown in Fig. 2 operates in a manner similar to thatshown in Fig. 1 except that upon the release'of relay III the circuitthrough the high resistance II is interrupted; consequently no currentwill flow through this resistance during the normal or idle condition ofthe circuit.

The equations for the charging of a condenser through a resistance aredeveloped in section 122 Charging a condenser through a resistance ofPrinciples of Electrical Engineering by Timbie and Bush and published byJohn Wiley and Sons, Inc. in 1923.

From Equation 40 on page 452 and the relation e=q/C the voltage 6 on thecondenser at any time t after the closure of the charging circuit of acompletely discharged condenser, i. e., a condenser having a zerovoltage Or charge between its plates, is

e =E('1-e RC1 where E is equal to the applied voltage, R is equal to thetotal resistance of the charging circuit, and C the capacity of thecondenser.

In case the condenser is initially charged to the voltage of the sourceE in the reverse direction the voltage across the condenser at any timet after the discharging and charging circuit closed The rate of changeof the voltage e with time determines accuracy or variation of the timerequired to reach any given potential.

If it is assumed that the same capacity and resistance are used in bothcircuits and that it is desired to have the same value of e or the samerate of change of c with respect to time, then 152:.693 RCA-t1. Thisrelationship may be developed as follows:

For charging from zero For discharging and charging from E Per cent {2increase 2 RC 2.69 RC 34 RC 2.19 RC 46 RC 1.69 RC 69 RC 1.44 RC 91 t RC1.14 RC 138 This improved arrangement thus gives a greater time delaywith a given size condenser and resistance. If it is desired the samedelay may be secured by a smaller RC product. The size of the condensermay be reduced or the value of the resistance reduced.

The value of the resistance used is usually fixed by the value of orchanges in the value of the leakage resistance of the condenser, input;circuit of the tube and related wiring. By means of this invention thevalue of the charging resistance may be reduced without reducing thetime delay of the circuit. Such a reduction of the charging resistancewill reduce the variation of the effective charging resistance and thusreduce the variation in the time delay of the circuit.

It is to be understood that the foregoing description of a specificembodiment of the invention is by way of example and that variousequivalent devices and apparatus may be substituted for the specificequipment shown as will be well understood by those skilled in the art.

What is claimed is:

1. A time delay device comprising a thermionic discharge device, aresponsive device connected in the output circuit thereof, a condenserconnected to the control circuit of said discharge device, a singlebattery for supplying anode po tential, filament current, and biaspotential for said device, circuits for initially charging the condenserto said battery potential, a single pole double throw switch arrangementfor completing the filament circuit of said device and for changing theconnections to said condenser for first discharging the condenser, andthen charging the condenser through a high impedance to the valuerequired to initiate a discharge through said thermionic dischargedevice to actuate said responsive device.

2. Time delay apparatus comprising a potential operated deviceresponsive to a predetermined potential, a condenser connected acrosssaid device for controlling the potential applied to said device inaccordance with the potential across said condenser, a source ofpotential and circuits for applying a reverse charge to said condenser,a single pole double throw switch for changing the connections to saidcondenser to first discharge the reverse charge on said condenserthrough a high impedance and then charge said condenser from said samesource of potential to said predetermined potential through a highimpedance.

3. Time delay apparatus comprising an electron discharging device havinga control element for initiating discharges therethrough when apredetermined potential is applied between said element and anotherelement of said device, a condenser connected across said elements forcontrolling the potential diil'erence between said elements, apparatusfor initially charging said condenser in a reverse direction, a singlesource of potential for supplying all the potential and energy for saiddevice and for charging said condenser, a high resistance, a singletransfer switch combination for changing the connections to saidcondenser for discharging it through said high resistance and thencharging it to the potential required to initiate a discharge throughsaid device.

4. Time delay apparatus comprising an electron discharge device having acontrol member for initiating discharges therethrough when apredetermined potential is applied to said member, a condenser forcontrolling the potential of said member, apparatus for initiallycharging said condenser in a reverse direction, a single source ofelectrical energy for supplying all the potential and energy for saiddevice and for charging said condenser, a high resistance, a single poledouble throw switch arrangement for changing the connections to saidcondenser for discharging it through said high resistance and thencharging it to the potential required to initiate a discharge throughsaid device, and an auxiliary switch controlled by said single poledouble throw switch for interrupting the circuit through said highresistance.

5. A time delay device comprising an electron discharge device having acathode, an anode, and a control element, a responsive device connectedin a circuit extending between said anode and the cathode, a condenserconnected between said cathode and said control element for controllingthe relative potentials of said elements, a single source of electricalenergy for supplying all the potentials supplied to said electrondischarge device, circuits for initially charging said condenser to saidbattery potential, a single transfer switch combination for changing theconnections to said condenser for first discharging said condenserthrough a high impedance and then charging said condenser in a reversedirection through said high impedance to the value required to initiatea discharge through said electron discharge device for actuating saidresponsive device.

6. A timing device comprising a single transfer switch combination theoperation of which initiates the operation of said timing device, aresponsive device operative a predetermined time interval after theoperation of said transfer device including a thermionic dischargedevice having a cathode, an anodefand acontroi electrode, a singlesource of potential for supplying energy to said thermionic device,circuit connections between said cathode, anode, responsivedevice, andthe source of potential for supplying anode potential to said dischargedevice, a condenser connected between said control element and saidcathode for controlling the relative potentials of said elements,circuit connections between said source of potential, said transferdevice and said condenser for charging said condenser to said batterypotential when said transfer device is not actuated, circuit connectionsbetween said discharge device and said condenser and said source ofpotential for energizing the cathode of said thermionic discharge deviceand changing the connections to said condenser through a high impedanceupon the actuation of said transfer switch for causing the charge ofsaid condenser to be first discharged through said high impedance andthen charged in a reverse direction also through said high impedance tothe potential required to initiate a discharge through said thermionicdischarge device and actuate said responsive device at the end of saidpredetermined interval of time.

ANDREW L. HOPPER.

